1. Field of the Invention
The present invention relates to controlling the spacing of a tape drive transducer such as a read head, a write head, or a read/write head relative to a magnetic data storage tape.
2. Background Art
Tape drive manufacturers are constantly challenged to produce tape drives with larger storage capacity to meet market demands. One way to accomplish this objective is to increase the storage density in the magnetic layer of the tape. By increasing the storage density, the tape may have more tracks for a given area and each track may have more bits.
An important factor affecting the accuracy of the read/write processes is magnetic spacing. The distance between the magnetic layer on the tape where the information is recorded and the transducer, or transducers, that write and read data is referred to as magnetic spacing. Magnetic spacing is a critical parameter because the amplitude of a playback signal decreases exponentially with increasing magnetic spacing. The decrease in amplitude caused by increased magnetic spacing may be referred to as Wallace spacing loss. Increased magnetic spacing increases the width of the read back pulse which leads to reduced data densities. The quality of the write operation also varies with spacing and decreased magnetic spacing improves the quality of the write operation. Decreased magnetic spacing requires the head to be closer to a major surface area of the tape during operation.
Magnetic spacing for a tape drive is currently set in the factory and continually changes during long term operation. After a sufficient period of time, a steady-state magnetic spacing develops. Magnetic spacing is generally designed to be in the range between 20-50 nm, depending upon product requirements. Generally, smaller magnetic spacing is capable of supporting higher data densities for a given read/write accuracy, while greater magnetic spacing is capable of supporting lower data densities for a given read/write accuracy. If a system is designed to run at high data densities, but the magnetic spacing is too large, an unacceptable drop in read/write accuracy will occur.
Pole tip recession (PTR) occurs as a transducer pole wears over time causing the pole to recede away from the tape and into the head. Pole tip recession increases the magnetic spacing between the magnetic fields in the magnetic layer of the tape and the transducer in the head. Each transducer in a tape drive has a unique magnetic spacing. Different transducers wear at different rates. In addition, the location of a transducer may result in different rates of pole tip recession.
Tape drives are designed to accommodate pole tip recession and the resultant degradation in performance. The need to design for pole tip recession results in designing for lower data storage densities than could be supported if the degradation could be prevented. Tape drives must be designed to provide an adequate margin for differences in transducer wear rates and positions which necessitates designing tape drives that have lower data storage capacity than could be provided if reduced spacing could be assured between the pole tips of the transducer and the tape. Greater storage capacities could also be achieved if there was a reliable and effective way to compensate for pole tip recession as the tape drive is used over time.
These and other problems are addressed by Applicant's invention as summarized below.